The "Destination (Port Unreachable)" error has two common triggers.
|Destination (Port Unreachable)
Possible causes and solutions
The Destination error may indicate a port problem. Using a different or unreserved port may correct this issue. Symptoms may include the call not being able to connect or the call unexpectedly disconnects after a short amount of time. The recommended course of action is to set all devices to use port 5060 which is the standard port used for SIP messaging.
Another possible cause is a call not successfully terminating. If one party leaves the call but the other party is not aware, it will continue to use the negotiated network ports despite there being no recipient for the traffic. This behavior will result in this message.